1. Field of the Invention
The subject invention relates to add in printed circuit cards ("PC cards") that provide I/O functions for computer based systems. More particularly, the invention relates to detecting certain events external to the PC card and using the same to trigger a modification of the power dissipation state of the PC card.
2. Description of the Prior Art
The PCMCIA (Personal Computer Memory Card International Association) standard was developed for the purpose of providing user installed memory and I/O functions for small form factor digital computer systems. The standard specifies a card containing a printed circuit board. This product is usually referred to as a PC card. There are three PC card formats: Types I, II and III. The standard specifies the interface between the PC card and the host. The hardware portion of the interface consists of a 68 position socket on one end of the card. The 68 position socket mates with a 68 position plug mounted on a header which is in turn mounted to a mother board or daughter board which is located inside the host. In addition to the hardware interface, the PCMCIA standard also specifies the signal timing protocol and software interface format.
The original Type I PC cards were intended to provide additional memory. No interaction with external devices was contemplated. Later, a PCMCIA specification for a type II card was developed which provided for I/O functionality such as modems, facsimile, network interfaces, multi-media interface, sound cards, etc. In order to handle I/O functions, a second connector is located on the end of the card opposite the 68 position socket. The I/O connector may be attached to the PC card either before or after the PC card is inserted into the host.
In operation, a PC card is plugged into the host. Upon insertion of the PC card, the host is interrupted and interrogates the PC card to access information needed to correctly configure both itself and the PC card. This process is called configuration. The PCMCIA standard specifies that the host cannot have access to the I/O functions of the PC card prior the completion of the configuration process.
In full operation, a PC card draws as much as 100 milliamperes of current. This is a problem if the host is a portable since at this rate a PC card would drain its host's battery in as little as two hours. To compound matters, as PC cards have become more popular, users are choosing to store their PC cards in the host. Of course, there is no problem when the host itself is powered down. But once the host is powered up, the high power dissipation of the I/O card begins.
Recognition of the need for power management for PC cards is not new. Others have worked at reducing P/C card power consumption by using low power consuming components and power management schemes based on software control.